Fixed spray sprinklers are well known which comprise a fixed spray nozzle that is threaded onto the top of a flow conduit. Both the nozzle and the conduit are considered "fixed" because they do not rotate about their axes during operation of the sprinkler. The nozzle might be adjustable to vary the spray. However, once the nozzle is initially adjusted to provide a particular spray, that spray covers a particular area of the ground without rotating or moving the spray relative to the ground. This characteristic gives rise to the term "fixed spray sprinkler".
U.S. Pat. No. 4,562,962 to Hartman discloses a fixed spray sprinkler of this type equipped with a flow shut off valve. The flow shut off valve comprises a poppet valve that is normally held open by a physical engagement with some portion of the sprinkler nozzle. If the sprinkler nozzle is broken or removed, the valve closes to prevent water from gushing out through the flow conduit. The valve is located adjacent the bottom of the flow conduit.
In fixed spray sprinklers, an array of flow conduits with different lengths are desirable to be able to position the nozzle at different heights above the ground. Since the Hartman shut off valve is held open by engaging against some portion of the nozzle, and since the shut off valve is adjacent the bottom of the flow conduit, the length of whatever is used to hold the shut off valve open must vary along with the length of the flow conduit. This greatly complicates the manufacture of sprinklers with such flow shut off valves, making such sprinklers more expensive.
In addition, many sprinkler manufacturers build and ship fixed spray sprinklers without pre-installed nozzles, but with a flush cap used on the top of the flow conduit in place of a nozzle. The flush cap prevents dirt or debris from entering the flow conduit during shipment and sprinkler installation. However, once the sprinkler is installed but before the flush cap is removed, the sprinkler system is pressurized for the first time. The flush cap is designed to let water exit or flush out through the cap during this initial pressurization to flush out any debris that might inadvertently have gotten inside the sprinkler. After this initial flush, the flush caps are removed and replaced with nozzles.
If flow shut off valves are installed inside the flow conduits, they will seal and shut off the flow during the initial pressurization of the system. Thus, the desired initial flush through the flush caps cannot occur. Accordingly, the use of flow shut off valves in fixed spray sprinklers is seemingly inconsistent with the use of flush caps. No fixed spray sprinklers having flush caps have ever been equipped with flow shut off valves.